The present invention relates to an optical fiber fusion splicer and an optical fiber fusion splicing method for fusion splicing two optical fibers of different mode field diameters using an electric arc discharge.
When structuring communication cable networks or manufacturing equipments using optical fibers, there are often instances where two optical fibers of mutually different mode field diameters are fusion spliced. In such a case, if an attempt is made to merely use an arc discharge fusion splicer to fusion splice these two optical fibers, a connection loss becomes larger than that of an instance where optical fibers of the same mode field diameters are connected to one another.
To address such an issue, in the state-of-the-art practice, various attempts have been made to connect two optical fibers of different mode field diameters to maintain the connection loss as low as possible. For instance, in an approach proposed in Japanese Patent Provisional Publication No. 2000-098171, when fusion splicing an optical fiber of a smaller mode field diameter on one hand and an optical fiber of a larger mode field diameter on the other hand, terminal ends of both the optical fibers are abutted to one another with abutted portions being fusion spliced using electric discharge heating and, thereafter, the electric discharge heating position is displaced from the abutted portions toward one of the optical fibers, of which mode field diameter is small, to apply additional electric discharge heating thereto in a reduced heating quantity to allow dopant of a core portion of the relevant optical fiber to be diffused for thereby permitting only the mode field diameter of the relevant optical fiber to be gradually enlarged in a lengthwise direction of the optical fiber.
Thus, by enlarging the mode field diameter of the relevant optical fiber of the smaller mode field diameter in a tapered shape, a substantial matching of mode field diameters of both the optical fibers at joint portions can be made, resulting in reduction of a connection loss. Also, the presence of an elongated tapered length enables connection of both the optical fibers with a limited increase in the connection loss that would be otherwise caused by a shortened tapered length, with a resultant further reduction in the connection loss.
Further, in Japanese Patent Provisional Publication No. 2000-275469, an alternative approach has been made in that, when establishing a matching of mode field diameters by applying additional electric discharge heating to an optical fiber of a small mode field diameter once fusion splicing operation has been conducted using an electric discharge heating, an attempt is made to obtain transmitted light images of the optical fibers after a fusion spliced condition, to estimate values of mode field diameters from brightness distribution curves and to estimate values of the mode field diameters of the optical fibers, one of which is applied with the additional heating using an estimated value for thereby observing a matching condition between the mode field diameters of both the optical fibers whereupon the additional heating is terminated when the matching condition is judged to fall in a sufficient range.
However, according to an aspect of the method proposed in Japanese Patent Provisional Publication No. 2000-098171, when fusion splicing the optical fibers of different mode field diameters, it is required to preliminarily find one of the two optical fibers, of which mode field diameter is small, and to set the optical fibers in fixed places. If such operation is wrongly carried out, then a reversed result appears, requiring nerves in fusion splicing operation.
With the approach proposed in Japanese Patent Provisional Publication No. 2000-275469, since the attempt is merely made to estimate the mode field diameters through image observations of the optical fibers to which the initial heating (fusion splicing heating) and the additional heating have been applied, there is a need for an operator to manually settle a travel distance in which the heating position is traveled toward the optical fiber of the smaller mode field diameter to be applied with the additional electric discharge heating, resulting in requirement not only in troublesome works but also in highly skilled experiences to achieve suitable settings with an inability in performing the splicing operation.
It is, therefore, a first object of the present invention to provide an improved optical fiber fusion splicer in which when splicing optical fibers of different mode field diameters, there is no need for an operator to set the optical fibers upon finding which optical fiber has a smaller mode field diameter and which is effective to automatically judge which settled optical fiber has the smaller mode field diameter to enable additional electric discharge heating to be applied to the relevant optical fiber of the smaller mode field diameter while automatically moving an electric discharge beam relative to the relevant optical fiber after electric discharge fusion heating.
It is a second object of the present invention to provide an improved optical fiber fusion splicer which when applying additional electric discharge heating to a relevant optical fiber while relatively moving an electric discharge beam thereto after fusion heating, enables a travel distance to be automatically optimized.
It is a third object of the present invention to provide an improved optical fiber fusion splicer which when applying additional electric discharge heating to a relevant optical fiber while causing an electric discharge beam to be relatively traveled after fusion splicing heating has been completed, enables a heating quantity to be automatically optimized.
It is a fourth object of the present invention to provide an optical fiber fusion splicing method in which when splicing optical fibers of different mode field diameters, there is no need for an operator to set the optical fibers upon finding one of the optical fibers, of which mode field diameter is small and in which judgment is automatically made to find one of the optical fibers settled, of which mode field diameter is small to enable additional electric discharge heating to be applied to the relevant optical fiber of the smaller mode field diameter and in such a way that a travel distance and a heating quantity are automatically optimized while automatically causing an electric discharge beam to be traveled relative to the relevant optical fiber after electric discharge fusion heating has been completed.
To address the above issues, according to a first aspect of the present invention, there is provided an optical fiber fusion splicer comprising an image pick up unit obtaining transmitted light images passing through side areas of abutted portions between two optical fibers of mutually different mode filed diameters, an image processing unit calculating mode field diameters of the respective optical fibers from brightness distributions of the images in terms of directions traverse to the optical fibers, an electric discharge heating unit applying electric discharge heating to the abutted portions with an electric arc discharge beam, a movable unit operative to move the electric arc discharge beam such that it travels relative to the abutted portions along an optical fiber axial direction, and a control unit controlling the electric discharge heating unit and the movable unit such that after conducting electric discharge fusion splicing heating to the abutted portions, a position of the electric arc discharge beam is traveled toward one of the optical fibers, of which mode field diameter is regarded to be small by the image processing unit, to apply additional electric discharge heating to the same to allow the mode field diameter of the relevant optical fiber to be enlarged.
Processing the transmitted light images due to lights passing through the side areas of the two optical fibers enables the respective mode field diameters to be calculated, providing a capability of automatically judging one of the optical fibers, of which mode filed diameter is small. For this reason, there is no need for an operator to preliminarily check which optical fiber has the smaller mode field diameter when setting the two optical fibers of the different mode field diameters to the fusion splicer and, even when these optical fibers are randomly set, the relevant optical fiber of the smaller mode field diameter is automatically detected, allowing the electric arc discharge beam position to be relatively traveled toward the detected optical fiber to apply the additional electric discharge heating thereto. Accordingly, it is possible to avoid an unfavorable result in that a difficulty is encountered in connecting the optical fibers at a low connection loss that would be otherwise caused by the absence of correct settings of the optical fibers due to operator""s mistake or misjudgment, releasing the operator""s need for using the nerve so as not to commit the mistake with a resultant reduction in load of the operator. Thus, it is possible for the electric arc discharge beam to be relatively traveled toward the relevant optical fiber of the smaller mode field diameter at all times to apply the additional electric discharge heating thereto regardless of the operator""s erroneous work for permitting the smaller mode field diameter to be enlarged at a minimized connection loss.
According to a second aspect of the present invention, there is provided an optical fiber fusion splicer which, in addition to the feature of the first aspect of the present invention set forth above, compels the image processing unit to obtain a diametric difference between the respective mode field diameters of the optical fibers, and the control unit controls a travel distance, in which the movable unit is to be traveled during the additional electric discharge heating, in dependence on the diametric difference between the respective mode field diameters.
Processing the transmitted light images due to lights passing through the side areas of the two optical fibers enables the respective mode field diameters to be obtained while providing a capability of automatically obtaining the difference between these diameters. There is a correlation between such a mode field diametric difference and the travel distance during the additional electric discharge heating for enlarging the mode field diameter at its optimum value, and such a correlation can be preliminarily obtained through experimental tests. This provides a capability of automatically controlling the travel distance at an optimum value during the electric discharge heating in dependence on the mode field diametric difference, enabling the smaller mode field diameter to be enlarged at an optimum value to improve the connection loss. Thus, it is possible for the operator, even who has no experience and knowledge, to simply splice the two optical fibers of different mode field diameters in a simple manner at the low connection loss.
According to a third aspect of the present invention, there is provided an optical fiber fusion splicer which, in addition to the feature of the first aspect of the present invention set forth above, allows the image processing unit to obtain a diametric difference between the respective mode field diameters of the optical fibers, and the control unit controls a heating quantity, to be applied to the relevant optical fiber with the electric discharge heating unit during the additional electric discharge heating, in dependence on the diametric difference between the respective mode field diameters.
Processing the transmitted light images due to lights passing through the side areas of the two optical fibers enables the respective mode field diameters to be obtained while providing a capability of automatically obtaining the difference between these diameters. There is a correlation between such a mode field diametric difference and the heating quantity during the additional electric discharge heating for enlarging the mode field diameter at its optimum value, and such a correlation can be preliminarily obtained through experimental tests. This provides a capability of automatically controlling the heating quantity at an optimum value during the electric discharge heating in dependence on the mode field diametric difference, enabling the smaller mode field diameter to be enlarged at an optimum value to improve the connection loss. Thus, it is possible for the operator, even in the absence of his experience and knowledge, to simply splice the two optical fibers of different mode field diameters in a simple manner at the low connection loss.
According to a fourth aspect of the present invention, there is provided an optical fiber fusion splicer which, in addition to the feature of the first aspect of the present invention set forth above, allows the control unit to be preliminarily stored with travel distances, in which the movable unit is to be traveled, and heating quantities, to be applied to the relevant optical fiber with the electric discharge heating unit, both of which are obtained in dependence on combinations between optical fibers of given mode field diameters and is operative to select one of the travel distances and one of the heating quantities in response to information obtained with the image processing unit.
Since the mode field diameters of the optical fibers are preliminarily standardized for each optical fiber under the standard, the presence of the travel distances and the electric discharge heating quantities specified for respective combinations of the optical fivers of varieties of kinds in a preliminary stage and stored in the control unit provides a capability for the control unit to select one of the travel distances and one of the heating quantities in response to information obtained from the image processing unit. By so doing, there is no need for the travel distance and the heating quantity to be calculated on site using the functions each for each combination of the optical fibers, providing a practical advantage.
According to a fifth aspect of the present invention, there is provided an optical fiber fusion splicer which, in addition to the feature of the first aspect of the present invention set forth above, allows the electric discharge heating unit to be operative to control a heating quantity to be applied during the additional electric discharge heating such that the larger a travel distance between the position of the electric arc discharge beam and a center of the abutted portions, the lower will be the heating quantity.
The heating quantity required during additional electric discharge heating may be preferably regulated such that the larger the distance between the position of the electric discharge beam and the center of abutted ends of the two optical fibers, the lower will be the heating quantity so as to gradually decrease the degree of enlargement of the relevant mode field diameter to form the tapered shape. To this end, control is performed such that the larger the distance between the position of the electric discharge beam and the center of the abutted ends of the two optical fibers, the lower will be the electric discharge current, or the larger the distance between the position of the electric discharge beam and the center of the abutted ends of the two optical fibers, the higher will be the traveling speed of the electric discharge beam. To this end, forming the control unit in a structure to enable the above-described control to be carried out according to information, related to the difference between the mode filed diameters of the optical fibers, transmitted from the image processing unit, it is possible to control the extent of dispersion of dopant of the core portion of the relevant optical fiber of the smaller mode field diameter at an optimum rate to achieve an idealistically tapered mode dispersion pattern.
According to a sixth aspect of the present invention, there is provided a method of fusion splicing optical fibers, which comprises processing transmitted light images obtained due to lights passing through side areas of abutted portions between two optical fibers of mutually different mode filed diameters to calculate mode field diameters of the respective optical fibers from brightness distributions of the images in terms of directions traverse to the optical fibers while obtaining a diametric difference between the two optical fibers, fusion splicing the abutted ends of both the optical fibers by applying an electric discharge fusion heating to the abutted portions using an electric arc discharge beam, and enlarging the mode field diameter of one of the optical fibers, of which mode field diameter is regarded to be small by an image processing unit, while traveling the electric arc discharge beam toward the relevant optical fiber of the small mode field diameter along an axial direction thereof and applying an additional electric discharge heating thereto in such a manner that a travel distance of the electric discharge beam and an electric discharge heating quantity are determined in dependence on the diametric difference.
Processing the transmitted light images due to lights passing through the side areas of the two optical fibers enables the respective mode field diameters to be calculated, providing a capability of automatically judging one of the optical fibers which has the smaller mode filed diameter. For this reason, there is no need for an operator to preliminarily check which optical fiber has the smaller mode field diameter when setting the two optical fibers of the different mode field diameters to the fusion splicer and, even when these optical fibers are randomly set, the relevant optical fiber of the smaller mode field diameter is automatically detected, allowing the electric discharge beam position to be relatively traveled toward the detected optical fiber to apply the additional electric discharge heating thereto. Further, the presence of a capability of automatically controlling the travel distance and the heating quantity during the electric discharge heating at optimum values in dependence on the mode field diametric difference enables the enlargement of the smaller mode field diameter at an optimum value to be easily realized for eliminating the connection loss regardless of the operator""s experience and capability.